The Mungari gold operation, fully-owned by Evolution Mining, comprises the White Foil open-pit mine and the Frog’s Leg underground mine along with a processing plant near Kalgoorlie in Western Australia.
The White Foil deposit was discovered in 1996 followed by the Frog’s Leg deposit in 1999. Limited open-pit mining operations were carried out at White Foil between 2002 and 2003 and at Frog’s Leg between 2003 and 2004.
In 2008, the Frog’s Leg mine transitioned to underground and the first gold pour was achieved the same year. Construction of a processing plant for the two mines was started in 2013 and completed the following year. The open-pit mining operations at White fall were also restarted in 2014.
Evolution Mining acquired the White Foil and the Frog’s Leg mines along with the Mungari processing plant from previous owner La Mancha Group International in August 2015.
Evolution Mining produced approximately 120,535 ounces (oz) of gold from the Mungari operation in 2019. It planned to invest up to £12m (A$22m) for the near-mine exploration drilling at Mungari in 2020.
Apart from aiming to extend the mine life by 10 years, the company is also investing on mine automation to increase production and reduce capital expenditure at Mungari.
Project location and geology
The Mungari gold operation is located approximately 20km west of Kalgoorlie and 600km east of the capital city of Perth in Western Australia.
The Frog’s Leg and White Foil deposits lie within the Norseman-Wiluna Greenstone Belt of the Yilgarn Craton, Western Australia.
The Mungari Shear zone borders the White Foil to the west within 3km, and is hosted within a quartz-rich gabbro unit which is part of the Powder Sill intrusive complex. The Frog’s Leg deposit lies within the sheared contact between the porphyritic cat rock and volcaniclastic rocks of Black Flag Beds.
Mineralisation and reserves
Mineralisation at the Mungari gold deposits occurs in quartz and stockwork veins. The White Foil mineralised zone is an open-depth deposit measuring 70m-wide and 400m-long. Mineralisation at Frog’s Leg occurs as sub-parallel ore lodes measuring between 2m and 20m in thickness.
The proven and probable ore reserves at the Mungari gold operation were estimated to be 11.63 million tonnes (Mt) grading 1.52g/t Au and containing 568 thousand ounces (koz) of gold metal as of December 2019.
The total mineral resources were estimated to be 50.92Mt, grading 1.47g/t Au and containing 2,409koz of gold.
Gold production at Mungari
The White Foil open-pit mine produced approximately 1.6Mt of ore containing 72koz of gold in 2019, while the Frog’s Leg underground mine produced 391 thousand tonnes (kt) of ore containing 48.5koz of gold during the same year.
Mining operations at Mungari
The open-pit mining operations at White Foil utilise conventional drill, blast, load, and haul methods with a maximum pit depth of 240m.
The mining fleet comprises one Hitachi EX2600, one Komatsu PC1250 and a Komatsu PC2000 excavator, seven Caterpillar 785C haul trucks, and two Caterpillar D10T dozers, apart from five Sandvik DP1500i top hammer drill rigs.
The underground mining operations at Frog’s Leg use the top-down bench stoping with paste fill method. The underground access is via a 5m x 5.5m decline which branches to twin declines at 125 metres below the surface (mbs). The deepest section of the mine currently lies at 700mbs.
The drilling equipment consists of a Sandvik DD421 twin-boom jumbo and two Sandvik DL421 production drills. The loading equipment includes two Caterpillar R2900G and one Caterpillar R1700G loaders with two Caterpillar AD55B dump trucks.
A new CAT R1700K underground loader was fitted with RCT’s ControlMaster® Guidance Automation system for the Frog’s Leg underground mining operation in August 2020. The underground loader is remotely operated from a ControlMaster® Automation Centre on the surface or designated sections of the mine.
The Mungari processing plant with a capacity of 1.6 million tonnes per annum (Mtpa) was commissioned in June 2014.
The run of mine (ROM) ore undergoes crushing in a primary jaw crusher followed by two more stages crushing in cone crushers. The crushed ore is stored in a bin and treated with lime before being introduced into the ball mill for grinding to a size of p80.
The finely ground ore undersize is passed on to a gravity concentrator to further remove foreign particles. The concentrate mineral product is then introduced into an intensive leach reactor to produce an elution which undergoes electrowinning in two carbon-in-leach (CIL) circuits to produce the final gold concentrate.
Perenti (formerly Ausdrill) is engaged to provide the surface mining, blasting and grade control drilling, explosive supply, and production drilling services for the Mungari gold operation.
RCT, a technology solutions company specialised in machine automation, provided the ControlMaster® Guidance Automation and associated systems for the automation of the at Frog’s Leg underground operations in 2020.
Sedgman was awarded the engineering, procurement, and construction (EPC) contract for the Mungari gold processing plant in February 2013.
Sedgman was also previously engaged in the feasibility studies as well as for the front-end engineering and design (FEED) studies of the project.
GCo Electrical was subcontracted by Sedgman for providing the electrical, instrumentation, and controls (EIC) systems for the processing plant.